A little over a year ago I made a new spear and made a pommel out of a racquetball for it, specifically as a kind of pommel-fighting pommel for spears. I love the thing and I've started doing it with all my poles. They didn't like it at Beltaine, but they've passed at every other event I've been to, and are perfectly safe IMO.
I just put up instructions on the wiki after getting a couple requests at WPO: Constructing a Racquetball Pommel.
I should be making another glaive in the next week or two and when I do I'll take pictures to put up, but it's pretty straight forward.
On a glaive they don't have much of an advantage over a regular pommel, other than being pretty. On a spear, though, you can put the pommel in the palm of your hand and push, giving you a nice strong thrust and a little extra reach. I don't use it on every shot, but it's a nice situational option to have available.